The lysine- and glutamic acid-rich protein KERP1 plays a role in Entamoeba histolytica liver abscess pathogenesis

A Review: Natural and Synthetic Compounds Targeting Entamoeba histolytica and Its Biological Membrane

Amoebiasis is the third most common parasitic cause of morbidity and mortality, particularly in countries with poor hygienic settings in central and south America, Africa, and India. This disease is caused by a protozoan parasite, namely Entamoeba histolytica, which infects approximately 50 million people worldwide, resulting in 70,000 deaths every year. Since the 1960s, E. histolytica infection has been successfully treated with metronidazole. However, there are drawbacks to metronidazole therapy: the side effects, duration of treatment, and need for additional drugs to prevent transmission. Previous interdisciplinary studies, including biophysics, bioinformatics, chemistry, and, more recently, lipidomics studies, have increased biomembranes’ publicity. The biological membranes are comprised of a mixture of membrane and cytosolic proteins. They work hand in hand mainly at the membrane part. They act as dedicated platforms for a whole range of cellular processes, such as cell proliferation, adhesion, migration, and intracellular trafficking, thus are appealing targets for drug treatment. Therefore, this review aims to observe the updated trend of the research regarding the biological membranes of E. histolytica from 2015 to 2021, which may help further research regarding the drug targeting the biological membrane.

Structural and Genetic Diversity of Entamoeba gingivalis Trophozoites Isolated from Diseased and Healthy Periodontal Sites

BACKGROUND: At present, there is little documented about the variability aspects of Entamoeba gingivalis (E. gingivalis) in relation to periodontal diseases. This is perhaps due to several specialists rejecting the notion that E. gingivalis can cause periodontal disease. AIM: The aim of the present study was to compare the morphological and genetic variability within trophozoites isolated from diseased (n = 26) and healthy periodontal sites (n = 14). METHODS: Detailed microscopic analyses were performed, in addition to post real-time polymerase chain reaction 18S-SSU rRNA gene scanning technology, using reference synthetic genes to analyze melting curve features from different isolates. RESULTS: All trophozoites isolated from diseased sites were significantly larger in size than those isolated from healthy sites. In addition, they were found in clusters, containing many leukophagocytosis and in a significantly higher number than those from healthy sites. Gene scanning revealed diversity within the isolates with a significantly higher number of mutant forms (18 out of 26) within the trophozoites isolated from diseased sites, 14 of them were of unknown origin. Four melting curves matched E. gingivalis H57 strain and the remaining eight were related to the wild strain (ATCC-30927). Isolates from healthy sites corresponded to the wild type (12 out of 14) with only two related to H57 strain. CONCLUSION: The study confirmed morphological and genetic variability between different isolates; We still recommend further in-depth molecular studies to investigate the role of this oral protozoan in the pathogenicity of periodontal affection. The study highlighted the importance of real engagement of multidisciplinary diagnostic strategies, involving experts from variable medical fields to reach truthful scientific outcomes concerning the association of certain microorganism to particular diseases or disorders.

ArfX2 GTPase Regulates Trafficking From the Trans-Golgi to Lysosomes and Is Necessary for Liver Abscess Formation in the Protozoan Parasite Entamoeba histolytica

Entamoeba histolytica is the causative agent of amoebic dysentery and liver abscess in humans. The parasitic lifestyle and the virulence of the protist require elaborate biological processes, including vesicular traffic and stress management against a variety of reactive oxygen and nitrogen species produced by the host immune response. Although the mechanisms for intracellular traffic of representative virulence factors have been investigated at molecular levels, it remains poorly understood whether and how intracellular traffic is involved in the defense against reactive oxygen and nitrogen species. Here, we demonstrate that EhArfX2, one of the Arf family of GTPases known to be involved in the regulation of vesicular traffic, was identified by comparative transcriptomic analysis of two isogenic strains: an animal-passaged highly virulent HM-1:IMSS Cl6 and in vitro maintained attenuated avirulent strain. EhArfX2 was identified as one of the most highly upregulated genes in the highly virulent strain. EhArfX2 was localized to small vesicle-like structures and largely colocalized with the marker for the trans-Golgi network SNARE, EhYkt6, but neither with the endoplasmic reticulum (ER)-resident chaperon, EhBip, nor the cis-Golgi SNARE, EhSed5, and Golgi-luminal galactosyl transferase, EhGalT. Expression of the dominant-active mutant form of EhArfX2 caused an increase in the number of lysosomes, while expression of the dominant-negative mutant led to a defect in lysosome formation and cysteine protease transport to lysosomes. Expression of the dominant-negative mutant in the virulent E. histolytica strain caused a reduction of the size of liver abscesses in a hamster model. This defect in liver abscess formation was likely at least partially attributed to reduced resistance to nitrosative, but not oxidative stress in vitro. These results showed that the EhArfX2-mediated traffic is necessary for the nitrosative stress response and virulence in the host.

Taxon-Specific Proteins of the Pathogenic Entamoeba Species E. histolytica and E. nuttalli

The human protozoan parasite Entamoeba histolytica can live in the human intestine for months or years without generating any symptoms in the host. For unknown reasons, amoebae can suddenly destroy the intestinal mucosa and become invasive. This can lead to amoebic colitis or extraintestinal amoebiasis whereby the amoebae spread to other organs via the blood vessels, most commonly the liver where abscesses develop. Entamoeba nuttalli is the closest genetic relative of E. histolytica and is found in wild macaques. Another close relative is E. dispar, which asyptomatically infects the human intestine. Although all three species are closely related, only E. histolytica and E. nuttalli are able to penetrate their host’s intestinal epithelium. Lineage-specific genes and gene families may hold the key to understanding differences in virulence among species. Here we discuss those genes found in E. histolytica that have relatives in only one or neither of its sister species, with particular focus on the peptidase, AIG, Ariel, and BspA families.

Golgi apparatus components in Entamoeba histolytica and Entamoeba dispar after monensin treatment

Highly dynamic ribosomes, glycogen granules, thinly fibrillar material, and multiple membrane-bound vesicles are embedded in the matrix-rich cytoplasm of Entamoeba spp. trophozoites. The absence of a Golgi apparatus in these amoebae has been commonly accepted. Here we challenge this observation by incubating Entamoeba histolytica and Entamoeba dispar with monensin, an ionophore that produces swelling of the Golgi apparatus. We observe changes in the trophozoites through standard transmission electron microscopy, cryofixation and cryosubstitution, and analyze the label and expression of known resident proteins of the cis-GM130 and trans-TGN38 Golgi network through confocal microscopy and Western blot assays. Cryosubstitution and standard methods using the treatment, preserved membranous lamellae resembling Golgi components. GM130 and TGN38 Golgi antigens were found by immunoelectron, immunoblot, and co-localization by confocal microscopy using the reagent NBD C6-ceramide. Our results indicate that previously undetected Golgi apparatus components are present in the cytoplasm of E. histolytica and E. dispar.

Genomic determinants for initiation and length of natural antisense transcripts in Entamoeba histolytica

Natural antisense transcripts (NAT) have been reported in prokaryotes and eukaryotes. While the functions of most reported NATs remain unknown, their potentials in regulating the transcription of their counterparts have been speculated. Entamoeba histolytica, which is a unicellular eukaryotic parasite, has a compact protein-coding genome with very short intronic and intergenic regions. The regulatory mechanisms of gene expression in this compact genome are under-described. In this study, by genome-wide mapping of RNA-Seq data in the genome of E. histolytica, we show that a substantial fraction of its protein-coding genes (28%) has significant transcription on their opposite strand (i.e. NAT). Intriguingly, we found the location of transcription start sites or polyadenylation sites of NAT are determined by the specific motifs encoded on the opposite strand of the gene coding sequences, thereby providing a compact regulatory system for gene transcription. Moreover, we demonstrated that NATs are globally up-regulated under various environmental conditions including temperature stress and pathogenicity. While NATs do not appear to be consequences of spurious transcription, they may play a role in regulating gene expression in E. histolytica, a hypothesis which needs to be tested.

Reassessing the Role of Entamoeba gingivalis in Periodontitis

The protozoan Entamoeba gingivalis resides in the oral cavity and is frequently observed in the periodontal pockets of humans and pets. This species of Entamoeba is closely related to the human pathogen Entamoeba histolytica, the agent of amoebiasis. Although E. gingivalis is highly enriched in people with periodontitis (a disease in which inflammation and bone loss correlate with changes in the microbial flora), the potential role of this protozoan in oral infectious diseases is not known. Periodontitis affects half the adult population in the world, eventually leads to edentulism, and has been linked to other pathologies, like diabetes and cardiovascular diseases. As aging is a risk factor for the disorder, it is considered an inevitable physiological process, even though it can be prevented and cured. However, the impact of periodontitis on the patient's health and quality of life, as well as its economic burden, are underestimated. Commonly accepted models explain the progression from health to gingivitis and then periodontitis by a gradual change in the identity and proportion of bacterial microorganisms in the gingival crevices. Though not pathognomonic, inflammation is always present in periodontitis. The recruitment of leukocytes to inflamed gums and their passage to the periodontal pocket lumen are speculated to fuel both tissue destruction and the development of the flora. The individual contribution to the disease of each bacterial species is difficult to establish and the eventual role of protozoa in the fate of this disease has been ignored. Following recent scientific findings, we discuss the relevance of these data and propose that the status of E. gingivalis be reconsidered as a potential pathogen contributing to periodontitis.

Life and Death of mRNA Molecules in Entamoeba histolytica

In eukaryotic cells, the life cycle of mRNA molecules is modulated in response to environmental signals and cell-cell communication in order to support cellular homeostasis. Capping, splicing and polyadenylation in the nucleus lead to the formation of transcripts that are suitable for translation in cytoplasm, until mRNA decay occurs in P-bodies. Although pre-mRNA processing and degradation mechanisms have usually been studied separately, they occur simultaneously and in a coordinated manner through protein-protein interactions, maintaining the integrity of gene expression. In the past few years, the availability of the genome sequence of Entamoeba histolytica, the protozoan parasite responsible for human amoebiasis, coupled to the development of the so-called “omics” technologies provided new opportunities for the study of mRNA processing and turnover in this pathogen. Here, we review the current knowledge about the molecular basis for splicing, 3′ end formation and mRNA degradation in amoeba, which suggest the conservation of events related to mRNA life throughout evolution. We also present the functional characterization of some key proteins and describe some interactions that indicate the relevance of cooperative regulatory events for gene expression in this human parasite.

Endoplasmic reticulum-resident Rab8A GTPase is involved in phagocytosis in the protozoan parasite Entamoeba histolytica

Phagocytosis is indispensable for the pathogenesis of the intestinal protozoan parasite Entamoeba histolytica. Here, we showed that in E. histolytica Rab8A, which is generally involved in trafficking from the trans‐Golgi network to the plasma membrane in other organisms but was previously identified in phagosomes of the amoeba in the proteomic analysis, primarily resides in the endoplasmic reticulum (ER) and participates in phagocytosis. We demonstrated that down‐regulation of EhRab8A by small antisense RNA‐mediated transcriptional gene silencing remarkably reduced adherence and phagocytosis of erythrocytes, bacteria and carboxylated latex beads. Surface biotinylation followed by SDS‐PAGE analysis revealed that the surface expression of several proteins presumably involved in target recognition was reduced in the EhRab8A gene‐silenced strain. Further, overexpression of wild‐type EhRab8A augmented phagocytosis, whereas expression of the dominant‐negative form of EhRab8A resulted in reduced phagocytosis. These results indicated that EhRab8A regulates transport of surface receptor(s) for the prey from the ER to the plasma membrane. To our knowledge, this is the first report that the ER‐resident Rab GTPase is involved in phagocytosis through the regulation of trafficking of a surface receptor, supporting a premise of direct involvement of the ER in phagocytosis.

Multinucleation and Polykaryon Formation is Promoted by the EhPC4 Transcription Factor in Entamoeba histolytica

Entamoeba histolytica is the intestinal parasite responsible for human amoebiasis that is a leading cause of death in developing countries. In this protozoan, heterogeneity in DNA content, polyploidy and genome plasticity have been associated to alterations in mechanisms controlling DNA replication and cell division. Studying the function of the transcription factor EhPC4, we unexpectedly found that it is functionally related to DNA replication, and multinucleation. Site-directed mutagenesis on the FRFPKG motif revealed that the K127 residue is required for efficient EhPC4 DNA-binding activity. Remarkably, overexpression of EhPC4 significantly increased cell proliferation, DNA replication and DNA content of trophozoites. A dramatically increase in cell size resulting in the formation of giant multinucleated trophozoites (polykaryon) was also found. Multinucleation event was associated to cytokinesis failure leading to abortion of ongoing cell division. Consistently, genome-wide profiling of EhPC4 overexpressing trophozoites revealed the up-regulation of genes involved in carbohydrates and nucleic acids metabolism, chromosome segregation and cytokinesis. Forced overexpression of one of these genes, EhNUDC (nuclear movement protein), led to alterations in cytokinesis and partially recapitulated the multinucleation phenotype. These data indicate for the first time that EhPC4 is associated with events related to polyploidy and genome stability in E. histolytica.

Immune Evasion Mechanisms of Entamoeba histolytica: Progression to Disease

Entamoeba histolytica (Eh) is a protozoan parasite that infects 10% of the world's population and results in 100,000 deaths/year from amebic dysentery and/or liver abscess. In most cases, this extracellular parasite colonizes the colon by high affinity binding to MUC2 mucin without disease symptoms, whereas in some cases, Eh triggers an aggressive inflammatory response upon invasion of the colonic mucosa. The specific host-parasite factors critical for disease pathogenesis are still not well characterized. From the parasite, the signature events that lead to disease progression are cysteine protease cleavage of the C-terminus of MUC2 that dissolves the mucus layer followed by Eh binding and cytotoxicity of the mucosal epithelium. The host mounts an ineffective excessive host pro-inflammatory response following contact with host cells that causes tissue damage and participates in disease pathogenesis as Eh escapes host immune clearance by mechanisms that are not completely understood. Ameba can modulate or destroy effector immune cells by inducing neutrophil apoptosis and suppressing respiratory burst or nitric oxide (NO) production from macrophages. Eh adherence to the host cells also induce multiple cytotoxic effects that can promote cell death through phagocytosis, apoptosis or by trogocytosis (ingestion of living cells) that might play critical roles in immune evasion. This review focuses on the immune evasion mechanisms that Eh uses to survive and induce disease manifestation in the host.

EhVps32 Is a Vacuole-Associated Protein Involved in Pinocytosis and Phagocytosis of Entamoeaba histolytica

Here, we investigated the role of EhVps32 protein (a member of the endosomal-sorting complex required for transport) in endocytosis of Entamoeba histolytica, a professional phagocyte. Confocal microscopy, TEM and cell fractionation revealed EhVps32 in cytoplasmic vesicles and also located adjacent to the plasma membrane. Between 5 to 30 min of phagocytosis, EhVps32 was detected on some erythrocytes-containing phagosomes of acidic nature, and at 60 min it returned to cytoplasmic vesicles and also appeared adjacent to the plasma membrane. TEM images revealed it in membranous structures in the vicinity of ingested erythrocytes. EhVps32, EhADH (an ALIX family member), Gal/GalNac lectin and actin co-localized in the phagocytic cup and in some erythrocytes-containing phagosomes, but EhVps32 was scarcely detected in late phagosomes. During dextran uptake, EhVps32, EhADH and Gal/GalNac lectin, but not actin, co-localized in pinosomes. EhVps32 recombinant protein formed oligomers composed by rings and filaments. Antibodies against EhVps32 monomers stained cytoplasmic vesicles but not erythrocytes-containing phagosomes, suggesting that in vivo oligomers are formed on phagosome membranes. The involvement of EhVps32 in phagocytosis was further study in pNeoEhvps32-HA-transfected trophozoites, which augmented almost twice their rate of erythrophagocytosis as well as the membranous concentric arrays built by filaments, spirals and tunnel-like structures. Some of these structures apparently connected phagosomes with the phagocytic cup. In concordance, the EhVps32-silenced G3 trophozoites ingested 80% less erythrocytes than the G3 strain. Our results suggest that EhVps32 participates in E. histolytica phagocytosis and pinocytosis. It forms oligomers on erythrocytes-containing phagosomes, probably as a part of the scission machinery involved in membrane invagination and intraluminal vesicles formation.

Trophozoites of E. histolytica represent an excellent model to study endosomal-sorting complex required for transport components due to their high endocytic activity and vesicle trafficking. The key role of EhVps32 on phagocytosis is supported by: i) its presence on phagosomes, ii) its interaction with EhADH (an erythrocytes receptor), Gal/GalNac lectin and actin, iii) the higher rate of erythrophagocytosis showed by EhVps32 overexpressing trophozoites, iv) the diminish rate of phagocytosis in EhVps32-silenced G3 trophozoites, and v) its location in erythrocytes-containing acidic phagosomes. Here, we discovered the presence of membranous concentric helicoidally and tunnel-like structures constituted by EhVps32 and EhADH that may have a dynamic role in membrane remodeling and in the generation of intraluminal vesicles in the phagosomes. Elucidating molecular mechanisms of endocytosis-exocytosis pathways will help us to better understand the pathogenic process of E. histolytica and develop new drugs for diagnosis and vaccine methods.

Evolutionary genomics and population structure of Entamoeba histolytica

Amoebiasis caused by the gastrointestinal parasite Entamoeba histolytica has diverse disease outcomes. Study of genome and evolution of this fascinating parasite will help us to understand the basis of its virulence and explain why, when and how it causes diseases. In this review, we have summarized current knowledge regarding evolutionary genomics of E. histolytica and discussed their association with parasite phenotypes and its differential pathogenic behavior. How genetic diversity reveals parasite population structure has also been discussed. Queries concerning their evolution and population structure which were required to be addressed have also been highlighted. This significantly large amount of genomic data will improve our knowledge about this pathogenic species of Entamoeba.

Peroxynitrite and peroxiredoxin in the pathogenesis of experimental amebic liver abscess

The molecular mechanisms by which Entamoeba histolytica causes amebic liver abscess (ALA) are still not fully understood. Amebic mechanisms of adherence and cytotoxic activity are pivotal for amebic survival but apparently do not directly cause liver abscess. Abundant evidence indicates that chronic inflammation (resulting from an inadequate immune response) is probably the main cause of ALA. Reports referring to inflammatory mechanisms of liver damage mention a repertoire of toxic molecules by the immune response (especially nitric oxide and reactive oxygen intermediates) and cytotoxic substances released by neutrophils and macrophages after being lysed by amoebas (e.g., defensins, complement, and proteases). Nevertheless, recent evidence downplays these mechanisms in abscess formation and emphasizes the importance of peroxynitrite (ONOO⁻). It seems that the defense mechanism of amoebas against ONOO⁻, namely, the amebic thioredoxin system (including peroxiredoxin), is superior to that of mammals. The aim of the present text is to define the importance of ONOO⁻ as the main agent of liver abscess formation during amebic invasion, and to explain the superior capacity of amoebas to defend themselves against this toxic agent through the peroxiredoxin and thioredoxin system.

Identification of the virulence landscape essential for Entamoeba histolytica invasion of the human colon

Entamoeba histolytica is the pathogenic amoeba responsible for amoebiasis, an infectious disease targeting human tissues. Amoebiasis arises when virulent trophozoites start to destroy the muco-epithelial barrier by first crossing the mucus, then killing host cells, triggering inflammation and subsequently causing dysentery. The main goal of this study was to analyse pathophysiology and gene expression changes related to virulent (i.e. HM1:IMSS) and non-virulent (i.e. Rahman) strains when they are in contact with the human colon. Transcriptome comparisons between the two strains, both in culture conditions and upon contact with human colon explants, provide a global view of gene expression changes that might contribute to the observed phenotypic differences. The most remarkable feature of the virulent phenotype resides in the up-regulation of genes implicated in carbohydrate metabolism and processing of glycosylated residues. Consequently, inhibition of gene expression by RNA interference of a glycoside hydrolase (β-amylase absent from humans) abolishes mucus depletion and tissue invasion by HM1:IMSS. In summary, our data suggest a potential role of carbohydrate metabolism in colon invasion by virulent E. histolytica.

The genome and transcriptome of the enteric parasite Entamoeba invadens, a model for encystation

Background

Several eukaryotic parasites form cysts that transmit infection. The process is found in diverse organisms such as Toxoplasma, Giardia, and nematodes. In Entamoeba histolytica this process cannot be induced in vitro, making it difficult to study. In Entamoeba invadens, stage conversion can be induced, but its utility as a model system to study developmental biology has been limited by a lack of genomic resources. We carried out genome and transcriptome sequencing of E. invadens to identify molecular processes involved in stage conversion.

Results

We report the sequencing and assembly of the E. invadens genome and use whole transcriptome sequencing to characterize changes in gene expression during encystation and excystation. The E. invadens genome is larger than that of E. histolytica, apparently largely due to expansion of intergenic regions; overall gene number and the machinery for gene regulation are conserved between the species. Over half the genes are regulated during the switch between morphological forms and a key signaling molecule, phospholipase D, appears to regulate encystation. We provide evidence for the occurrence of meiosis during encystation, suggesting that stage conversion may play a key role in recombination between strains.

Conclusions

Our analysis demonstrates that a number of core processes are common to encystation between distantly related parasites, including meiosis, lipid signaling and RNA modification. These data provide a foundation for understanding the developmental cascade in the important human pathogen E. histolytica and highlight conserved processes more widely relevant in enteric pathogens.

The alphabet of intrinsic disorder: II. Various roles of glutamic acid in ordered and intrinsically disordered proteins

The ability of a protein to fold into unique functional state or to stay intrinsically disordered is encoded in its amino acid sequence. Both ordered and intrinsically disordered proteins (IDPs) are natural polypeptides that use the same arsenal of 20 proteinogenic amino acid residues as their major building blocks. The exceptional structural plasticity of IDPs, their capability to exist as heterogeneous structural ensembles and their wide array of important disorder-based biological functions that complements functional repertoire of ordered proteins are all rooted within the peculiar differential usage of these building blocks by ordered proteins and IDPs. In fact, some residues (so-called disorder-promoting residues) are noticeably more common in IDPs than in sequences of ordered proteins, which, in their turn, are enriched in several order-promoting residues. Furthermore, residues can be arranged according to their “disorder promoting potencies,” which are evaluated based on the relative abundances of various amino acids in ordered and disordered proteins. This review continues a series of publications on the roles of different amino acids in defining the phenomenon of protein intrinsic disorder and concerns glutamic acid, which is the second most disorder-promoting residue.

The α-helical regions of KERP1 are important in Entamoeba histolytica adherence to human cells

The lysine and glutamic acid rich protein KERP1 is a unique surface adhesion factor associated with virulence in the human pathogen Entamoeba histolytica. Both the function and structure of this protein remain unknown to this date. Here, we used circular dichroism, analytical ultracentrifugation and bioinformatics modeling to characterize the structure of KERP1. Our findings revealed that it is an α-helical rich protein organized as a trimer, endowed with a very high thermal stability (Tm = 89.6°C). Bioinformatics sequence analyses and 3D-structural modeling indicates that KERP1 central segments could account for protein trimerization. Relevantly, expressing the central region of KERP1 in living parasites, impair their capacity to adhere to human cells. Our observations suggest a link between the inhibitory effect of the isolated central region and the structural features of KERP1.

Peroxiredoxins in parasites

SIGNIFICANCE

Parasite survival and virulence relies on effective defenses against reactive oxygen and nitrogen species produced by the host immune system. Peroxiredoxins (Prxs) are ubiquitous enzymes now thought to be central to such defenses and, as such, have potential value as drug targets and vaccine antigens.

RECENT ADVANCES

Plasmodial and kinetoplastid Prx systems are the most extensively studied, yet remain inadequately understood. For many other parasites our knowledge is even less well developed. Through parasite genome sequencing efforts, however, the key players are being discovered and characterized. Here we describe what is known about the biochemistry, regulation, and cell biology of Prxs in parasitic protozoa, helminths, and fungi. At least one Prx is found in each parasite with a sequenced genome, and a notable theme is the common patterns of expression, localization, and functionality among sequence-similar Prxs in related species.

CRITICAL ISSUES

The nomenclature of Prxs from parasites is in a state of disarray, causing confusion and making comparative inferences difficult. Here we introduce a systematic Prx naming convention that is consistent between organisms and informative about structural and evolutionary relationships.

FUTURE DIRECTIONS

The new nomenclature should stimulate the crossfertilization of ideas among parasitologists and with the broader redox research community. The diverse parasite developmental stages and host environments present complex systems in which to explore the variety of roles played by Prxs, with a view toward parlaying what is learned into novel therapies and vaccines that are urgently needed.

Host-Parasite interactions in Entamoeba histolytica and Entamoeba dispar: what have we learned from their genomes?

Invasive amoebiasis caused by Entamoeba histolytica is a major global health problem. Virulence is a rare outcome of infection, occurring in fewer than 1 in 10 infections. Not all strains of the parasite are equally virulent, and understanding the mechanisms and causes of virulence is an important goal of Entamoeba research. The sequencing of the genome of E. histolytica and the related avirulent species Entamoeba dispar has allowed whole-genome-scale analyses of genetic divergence and differential gene expression to be undertaken. These studies have helped elucidate mechanisms of virulence and identified genes differentially expressed in virulent and avirulent parasites. Here, we review the current status of the E. histolytica and E. dispar genomes and the findings of a number of genome-scale studies comparing parasites of different virulence.

Endoplasmic reticulum stress-sensing mechanism is activated in Entamoeba histolytica upon treatment with nitric oxide

The Endoplasmic Reticulum stores calcium and is a site of protein synthesis and modification. Changes in ER homeostasis lead to stress responses with an activation of the unfolded protein response (UPR). The Entamoeba histolytica endomembrane system is simple compared to those of higher eukaryotes, as a canonical ER is not observed. During amoebiasis, an infection of the human intestine and liver by E. histolytica, nitric oxide (NO) triggers an apoptotic-like event preceded by an impairment of energy production and a loss of important parasite pathogenic features. We address the question of how this ancient eukaryote responds to stress induced by immune components (i.e. NO) and whether stress leads to ER changes and subsequently to an UPR. Gene expression analysis suggested that NO triggers stress responses marked by (i) dramatic up-regulation of hsp genes although a bona fide UPR is absent; (ii) induction of DNA repair and redox gene expression and iii) up-regulation of glycolysis-related gene expression. Enzymology approaches demonstrate that NO directly inhibits glycolysis and enhance cysteine synthase activity. Using live imaging and confocal microscopy we found that NO dramatically provokes extensive ER fragmentation. ER fission in E. histolytica appears as a protective response against stress, as it has been recently proposed for neuron self-defense during neurologic disorders. Chronic ER stress is also involved in metabolic diseases including diabetes, where NO production reduces ER calcium levels and activates cell death. Our data highlighted unique cellular responses of interest to understand the mechanisms of parasite death during amoebiasis.

Towards the establishment of a porcine model to study human amebiasis

BACKGROUND

Entamoeba histolytica is an important parasite of the human intestine. Its life cycle is monoxenous with two stages: (i) the trophozoite, growing in the intestine and (ii) the cyst corresponding to the dissemination stage. The trophozoite in the intestine can live as a commensal leading to asymptomatic infection or as a tissue invasive form producing mucosal ulcers and liver abscesses. There is no animal model mimicking the whole disease cycle. Most of the biological information on E. histolytica has been obtained from trophozoite adapted to axenic culture. The reproduction of intestinal amebiasis in an animal model is difficult while for liver amebiasis there are well-described rodent models. During this study, we worked on the assessment of pigs as a new potential model to study amebiasis.

METHODOLOGY/PRINCIPAL FINDINGS

We first co-cultured trophozoites of E. histolytica with porcine colonic fragments and observed a disruption of the mucosal architecture. Then, we showed that outbred pigs can be used to reproduce some lesions associated with human amebiasis. A detailed analysis was performed using a washed closed-jejunal loops model. In loops inoculated with virulent amebas a severe acute ulcerative jejunitis was observed with large hemorrhagic lesions 14 days post-inoculation associated with the presence of the trophozoites in the depth of the mucosa in two out four animals. Furthermore, typical large sized hepatic abscesses were observed in the liver of one animal 7 days post-injection in the portal vein and the liver parenchyma.

CONCLUSIONS

The pig model could help with simultaneously studying intestinal and extraintestinal lesion development.

Glucose starvation boosts Entamoeba histolytica virulence

The unicellular parasite, Entamoeba histolytica, is exposed to numerous adverse conditions, such as nutrient deprivation, during its life cycle stages in the human host. In the present study, we examined whether the parasite virulence could be influenced by glucose starvation (GS). The migratory behaviour of the parasite and its capability to kill mammalian cells and to lyse erythrocytes is strongly enhanced following GS. In order to gain insights into the mechanism underlying the GS boosting effects on virulence, we analyzed differences in protein expression levels in control and glucose-starved trophozoites, by quantitative proteomic analysis. We observed that upstream regulatory element 3-binding protein (URE3-BP), a transcription factor that modulates E.histolytica virulence, and the lysine-rich protein 1 (KRiP1) which is induced during liver abscess development, are upregulated by GS. We also analyzed E. histolytica membrane fractions and noticed that the Gal/GalNAc lectin light subunit LgL1 is up-regulated by GS. Surprisingly, amoebapore A (Ap-A) and cysteine proteinase A5 (CP-A5), two important E. histolytica virulence factors, were strongly down-regulated by GS. While the boosting effect of GS on E. histolytica virulence was conserved in strains silenced for Ap-A and CP-A5, it was lost in LgL1 and in KRiP1 down-regulated strains. These data emphasize the unexpected role of GS in the modulation of E.histolytica virulence and the involvement of KRiP1 and Lgl1 in this phenomenon.

During infection, pathogens are exposed to different environmental stresses that are mostly the consequence of the host immune defense. The most studied of these environmental stresses are the response of pathogens to nitric oxide and to hydrogen peroxide, both produced by phagocytes. In contrast, the overall knowledge about the response of pathogens to metabolic stresses is scanty. Amebiasis is caused by the unicellular protozoan parasite Entamoeba histolytica, and has a worldwide distribution with substantial morbidity and mortality. During its journey in the host, the parasite is exposed to the host immune system and to variations in nutrient availability due to the host nutrition status and the competition with the bacterial flora of the large intestine. How E. histolytica responds to glucose starvation (GS) has never been investigated. Here, the authors report that the parasite virulence is boosted by GS. Paradoxically, two well accepted virulence factors, the amoebapore A and the cysteine protease A5 are less abundant in the glucose-starved parasites. This Accordingly, these proteins are not required for the boosting of the E. histolytica virulence, in contrast to KRiP1 and LgL1 that seem to be involved in this phenomenon.

N-terminal Gly(224)-Gly(411) domain in Listeria adhesion protein interacts with host receptor Hsp60

BACKGROUND

Listeria adhesion protein (LAP) is a housekeeping bifunctional enzyme consisting of N-terminal acetaldehyde dehydrogenase (ALDH) and C-terminal alcohol dehydrogenase (ADH). It aids Listeria monocytogenes in crossing the epithelial barrier through a paracellular route by interacting with its host receptor, heat shock protein 60 (Hsp60). To gain insight into the binding interaction between LAP and Hsp60, LAP subdomain(s) participating in the Hsp60 interaction were investigated.

METHODS

Using a ModBase structural model, LAP was divided into 4 putative subdomains: the ALDH region contains N1 (Met(1)-Pro(223)) and N2 (Gly(224)-Gly(411)), and the ADH region contains C1 (Gly(412)-Val(648)) and C2 (Pro(649)-Val(866)). Each subdomain was cloned and overexpressed in Escherichia coli and purified. Purified subdomains were used in ligand overlay, immunofluorescence, and bead-based epithelial cell adhesion assays to analyze each domain's affinity toward Hsp60 protein or human ileocecal epithelial HCT-8 cells.

RESULTS

The N2 subdomain exhibited the greatest affinity for Hsp60 with a K(D) of 9.50±2.6 nM. The K(D) of full-length LAP (7.2±0.5 nM) to Hsp60 was comparable to the N2 value. Microspheres (1 µm diameter) coated with N2 subdomain showed significantly (P<0.05) higher binding to HCT-8 cells than beads coated with other subdomains and this binding was inhibited when HCT-8 cells were pretreated with anti-Hsp60 antibody to specifically block epithelial Hsp60. Furthermore, HCT-8 cells pretreated with purified N2 subdomain also reduced L. monocytogenes adhesion by about 4 log confirming its involvement in interaction with epithelial cells.

CONCLUSION

These data indicate that the N2 subdomain in the LAP ALDH domain is critical in initiating interaction with mammalian cell receptor Hsp60 providing insight into the molecular mechanism of pathogenesis for the development of potential anti-listerial control strategies.

Tissue destruction and invasion by Entamoeba histolytica

Entamoeba histolytica is the causative agent of amebiasis, a disease that is a major source of morbidity and mortality in the developing world. The potent cytotoxic activity of the parasite appears to underlie disease pathogenesis, although the mechanism is unknown. Recently, progress has been made in determining that the parasite activates apoptosis in target cells and some putative effectors have been identified. Recent studies have also begun to unravel the host genetic determinants that influence infection outcome. Thus, we are beginning to get a clearer picture of how this parasite manages to infect, invade and ultimately inflict devastating tissue destruction.

A Sequential Model of Host Cell Killing and Phagocytosis by Entamoeba histolytica

The protozoan parasite Entamoeba histolytica is responsible for invasive intestinal and extraintestinal amebiasis. The virulence of Entamoeba histolytica is strongly correlated with the parasite's capacity to effectively kill and phagocytose host cells. The process by which host cells are killed and phagocytosed follows a sequential model of adherence, cell killing, initiation of phagocytosis, and engulfment. This paper presents recent advances in the cytolytic and phagocytic processes of Entamoeba histolytica in context of the sequential model.

The domain structure of Entamoeba α-actinin2

Entamoeba histolytica, a major agent of human amoebiasis, expresses two distinct forms of α-actinin, a ubiquitous actin-binding protein that is present in most eukaryotic organisms. In contrast to all metazoan α-actinins, in both isoforms the intervening rod domain that connects the N-terminal actin-binding domain with the C-terminal EF-hands is much shorter. It is suggested that these α-actinins may be involved in amoeboid motility and phagocytosis, so we cloned and characterised each domain of one of these α-actinins to better understand their functional role. The results clearly showed that the domains have properties very similar to those of conventional α-actinins.

Detection of the Endosomal Sorting Complex Required for Transport in Entamoeba histolytica and Characterization of the EhVps4 Protein

Eukaryotic endocytosis involves multivesicular bodies formation, which is driven by endosomal sorting complexes required for transport (ESCRT). Here, we showed the presence and expression of homologous ESCRT genes in Entamoeba histolytica. We cloned and expressed the Ehvps4 gene, an ESCRT member, to obtain the recombinant EhVps4 and generate specific antibodies, which immunodetected EhVps4 in cytoplasm of trophozoites. Bioinformatics and biochemical studies evidenced that rEhVps4 is an ATPase, whose activity depends on the conserved E211 residue. Next, we generated trophozoites overexpressing EhVps4 and mutant EhVps4-E211Q FLAG-tagged proteins. The EhVps4-FLAG was located in cytosol and at plasma membrane, whereas the EhVps4-E211Q-FLAG was detected as abundant cytoplasmic dots in trophozoites. Erythrophagocytosis, cytopathic activity, and hepatic damage in hamsters were not improved in trophozoites overexpressing EhVps4-FLAG. In contrast, EhVps4-E211Q-FLAG protein overexpression impaired these properties. The localization of EhVps4-FLAG around ingested erythrocytes, together with our previous results, strengthens the role for EhVps4 in E. histolytica phagocytosis and virulence.

Use of bacterially expressed dsRNA to downregulate Entamoeba histolytica gene expression

Background

Modern RNA interference (RNAi) methodologies using small interfering RNA (siRNA) oligonucleotide duplexes or episomally synthesized hairpin RNA are valuable tools for the analysis of gene function in the protozoan parasite Entamoeba histolytica. However, these approaches still require time-consuming procedures including transfection and drug selection, or costly synthetic molecules.

Principal Findings

Here we report an efficient and handy alternative for E. histolytica gene down-regulation mediated by bacterial double-stranded RNA (dsRNA) targeting parasite genes. The Escherichia coli strain HT115 which is unable to degrade dsRNA, was genetically engineered to produce high quantities of long dsRNA segments targeting the genes that encode E. histolytica β-tubulin and virulence factor KERP1. Trophozoites cultured in vitro were directly fed with dsRNA-expressing bacteria or soaked with purified dsRNA. Both dsRNA delivery methods resulted in significant reduction of protein expression. In vitro host cell-parasite assays showed that efficient downregulation of kerp1 gene expression mediated by bacterial dsRNA resulted in significant reduction of parasite adhesion and lytic capabilities, thus supporting a major role for KERP1 in the pathogenic process. Furthermore, treatment of trophozoites cultured in microtiter plates, with a repertoire of eighty-five distinct bacterial dsRNA segments targeting E. histolytica genes with unknown function, led to the identification of three genes potentially involved in the growth of the parasite.

Conclusions

Our results showed that the use of bacterial dsRNA is a powerful method for the study of gene function in E. histolytica. This dsRNA delivery method is also technically suitable for the study of a large number of genes, thus opening interesting perspectives for the identification of novel drug and vaccine targets.

Using differential gene expression to study Entamoeba histolytica pathogenesis

The release of the Entamoeba histolytica genome has facilitated the development of techniques to survey rapidly and to relate gene expression with biology. The association and potential contribution of differential gene expression to the life cycle and the virulence of this protozoan parasite of humans are reviewed here.

Host-microbe interactions and defense mechanisms in the development of amoebic liver abscesses

SUMMARY

Amoebiasis by Entamoeba histolytica is a major public health problem in developing countries and leads to several thousand deaths per year. The parasite invades the intestine (provoking diarrhea and dysentery) and the liver, where it forms abscesses (amoebic liver abscesses [ALAs]). The liver is the organ responsible for filtering blood coming from the intestinal tract, a task that implies a particular structure and immune features. Amoebae use the portal route and break through the sinusoidal endothelial barrier to reach the hepatic parenchyma. When faced with systemic and cell-mediated defenses, trophozoites adapt to their new environment and modulate host responses, leading to parasite survival and the formation of inflammatory foci. Cytopathogenic effects and the onset of inflammation may be caused by diffusible products originating from parasites and/or immune cells either by their secretion or by their release after cell death. Liver infection thus results from the interplay between E. histolytica and hepatic cells. Despite its importance in terms of public health burden, the lack of integrated data on ALA genesis means that we have only an incomplete description of the initiation and development of hepatic amoebiasis. Here, we review the main steps of ALA development as well as the responses triggered in both the host and the parasite. Transcriptome studies highlighted parasite factors involved in adherence to human cells, cytopathogenic effects, and adaptative and stress responses. An understanding of their role in ALA development will help to unravel the host-pathogen interactions and their evolution throughout the infection.

New insights into Entamoeba histolytica pathogenesis

PURPOSE OF REVIEW

Entamoeba histolytica is an important global pathogen and a leading cause of parasitic death worldwide. This article summarizes significant research findings over the last year.

RECENT FINDINGS

Efforts have focused primarily on identification of novel virulence determinants in E. histolytica, transcriptional profiling during tissue invasion and stage conversion, and characterization of basic cell biological processes. Additionally, new techniques for gene silencing have been identified.

SUMMARY

A comprehensive examination of the parasite lifestyle on a whole genome level has been undertaken, allowing identification of new virulence genes and signaling pathways and processes relevant to amebic biology.

Recent insights into Entamoeba development: identification of transcriptional networks associated with stage conversion

Entamoeba histolytica is an important human pathogen and a leading parasitic cause of death globally. The parasite life cycle alternates between the trophozoite form, which is motile and causes invasive disease and the cyst stage, which is environmentally resistant and transmits infection. Understanding the triggers that initiate stage conversion is an important yet understudied area of investigation. Recent progress in dissecting the transcriptional networks that regulate E. histolytica development is outlined in this paper.

Entamoeba histolytica modulates a complex repertoire of novel genes in response to oxidative and nitrosative stresses: implications for amebic pathogenesis

Upon host infection, the protozoan parasite Entamoeba histolytica is confronted with reactive oxygen and nitrogen species and must survive these stresses in order to cause invasive disease. We analysed the parasite's response to oxidative and nitrosative stresses, probing the transcriptional changes of trophozoites of a pathogenic strain after a 60 min exposure to H2O2 (1 mM) or a NO donor (dipropylenetriamine-NONOate, 200 microM), using whole-genome DNA microarrays. Genes encoding reactive oxygen and nitrogen species detoxification enzymes had high transcriptional levels under basal conditions and upon exposure to both stresses. On a whole-genome level, there was significant modulation of gene expression by H2O2 (286 genes regulated) and dipropylenetriamine-NONOate (1036 genes regulated) with a significant overlap of genes modulated under both conditions (164 genes). A number of transcriptionally regulated genes were in signalling/regulatory and repair/metabolic pathways. However, the majority of genes with altered transcription encode unknown proteins, suggesting as yet unraveled response pathways in E. histolytica. Trophozoites of a non-pathogenic E. histolytica strain had a significantly muted transcriptional response to H2O2 compared with the pathogenic strain, hinting that differential response to oxidative stress may be one factor that contributes to the pathogenic potential of E. histolytica.

Identification of an Entamoeba histolytica serine-, threonine-, and isoleucine-rich protein with roles in adhesion and cytotoxicity

Entamoeba histolytica is a leading cause of parasitic death globally. However, the molecular framework regulating pathogenesis is poorly understood. We have previously used expression profiling to identify Entamoeba genes whose expressions were strictly associated with virulent strains (R. C. MacFarlane and U. Singh, Infect. Immun. 74:340-351, 2006). One gene, which we have named EhSTIRP (Entamoeba histolytica serine-, threonine-, and isoleucine-rich protein), was exclusively expressed in virulent but not in nonvirulent Entamoeba strains. EhSTIRP is predicted to be a transmembrane protein and is encoded by a multigene family. In order to characterize its function in amebic biology, we used a double-stranded RNA-based approach and were able to selectively down-regulate expression of this gene family. Upon EhSTIRP down-regulation, we were able to ascribe cytotoxic and adhesive properties to the protein family using lactate dehydrogenase release and Chinese hamster ovary cell adhesion assays. EhSTIRP thus likely represents a novel determinant of virulence in Entamoeba histolytica. This work validates the fact that genes expressed exclusively in virulent strains may represent virulence determinants and highlights the need for further functional analyses of other genes with similar expression profiles.